1. Field of Invention
The present invention relates generally to holographic laser scanners of ultra-compact design capable of reading bar code symbols in point-of-sale (POS) and other demanding scanning environments.
2. Brief Description of the Prior Art
The use of bar code symbols for product and article identification is well known in the art.
Presently, various types of bar code symbol scanners have been developed. In general, these bar code symbol readers can be classified into two distinct classes.
The first class of bar code symbol reader simultaneously illuminates all of the bars and spaces of a bar code symbol with light of a specific wavelength(s) in order to capture an image thereof for recognition and decoding purposes. Such scanners are commonly known as CCD scanners because they use CCD image detectors to detect images of the bar code symbols being read.
The second class of bar code symbol reader uses a focused light beam, typically a focused laser beam, to sequentially scan the bars and spaces of a bar code symbol to be read. This type of bar code symbol scanner is commonly called a xe2x80x9cflying spotxe2x80x9d scanner as the focused laser beam appears as xe2x80x9ca spot of light that fliesxe2x80x9d across the bar code symbol being read. In general, laser bar code symbol scanners are subclassified further by the type of mechanism used to focus and scan the laser beam across bar code symbols.
The majority of laser scanners in use today, particular in retail environments, employ lenses and moving (i.e. rotating or oscillating) mirrors and/or other optical elements in order to focus and scan laser beams across bar code symbols during code symbol reading operations. In demanding retail scanning environments, it is common for such systems to have both bottom and side scanning windows to enable highly aggressive scanner performance, whereby the cashier need only drag a bar coded product past these scanning windows for the bar code thereon to be automatically read with minimal assistance of the cashier or checkout personal. Such dual scanning window systems are typically referred to as xe2x80x9cbiopticalxe2x80x9d laser scanning systems as such systems employ two sets of optics disposed behind the bottom and side scanning windows thereof. Examples of polygon-based bioptical laser scanning systems are disclosed in U.S. Pat. Nos. 4,229,588 and 4,652,732, assigned to NCR, Inc., each incorporated herein by reference in its entirety.
In general, prior art bioptical laser scanning systems are generally more aggressive that conventional single scanning window systems. For this reason, bioptical scanning system are often deployed in demanding retail environments, such as supermarkets and high-volume department stores, where high check-out throughput is critical to achieving store profitability and customer satisfaction.
While prior art bioptical scanning systems represent a technological advance over most single scanning window system, prior art bioptical scanning systems in general suffered from various shortcomings and drawbacks.
In particular, by virtue of the dual scanning windows and supporting optics required by prior art bioptical laser scanning systems, such scanning systems have been physically larger than many retail environments would otherwise desire, as space near the point-of-sale is the most valuable space within the retail environment. Also, the laser scanning patterns of prior art bioptical laser scanning systems are not optimized in terms of scanning coverage and performance, and are generally expensive to manufacture by virtue of the large number of optical components presently required to constructed such laser scanning systems.
Thus, there is a great need in the art for an improved bioptical-type laser scanning bar code symbol reading system, while avoiding the shortcomings and drawbacks of prior art laser scanning systems and methodologies.
Accordingly, a primary object of the present invention is to provide a novel bioptical-type holographic laser scanning system which is free of the shortcomings and drawbacks of prior art bioptical laser scanning systems and methodologies.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein a plurality of pairs of quasi-orthogonal laser scanning planes are projected within predetermined regions of space contained within a 3-D scanning volume defined between the bottom and side scanning windows of the system.
Another object of the present invention is to provide a novel bioptical holographic laser scanning system, wherein the plurality of pairs of quasi-orthogonal laser scanning planes are produced using a holographic scanning disc having holographic scanning facets that have high and low elevation angle characteristics as well as left, right and zero skew angle characteristics.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein the each pair of quasi-orthogonal laser scanning planes comprises a plurality of substantially-vertical laser scanning planes for reading bar code symbols having bar code elements (i.e. ladder-type bar code symbols) that are oriented substantially horizontal with respect to the bottom scanning window, and a plurality of substantially-horizontal laser scanning planes for reading bar code symbols having bar code elements (i.e. picket-fence type bar code symbols) that are oriented substantially vertical with respect to the bottom scanning window.
Another object of the present invention is to provide a bioptical holographic laser scanning system comprising a plurality of laser scanning stations, each of which produces a plurality of pairs of quasi-orthogonal laser scanning planes are projected within predetermined regions of space contained within a 3-D scanning volume defined between the bottom and side scanning windows of the system.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein the plurality of pairs of quasi-orthogonal laser scanning planes are produced using a holographic scanning disc supporting holographic scanning facets having high and low elevation angle characteristics and left, right and zero skew angle characteristics.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein each laser scanning station produces a plurality of pairs of quasi-orthogonal laser scanning planes which can read bar code symbol that is orientated with bar code elements arranged in either a substantially vertical (i.e. picket-fence) or substantially horizontal (i.e. ladder) configuration with respect to the horizontal scanning window of the system.
Another object of the present invention is to provide such a bioptical holographic laser scanning system employing four laser scanning systems, wherein the first and third laser scanning stations employ mirror groups and scanning facets having only high elevation characteristics and left and right skew angle characteristics so as to produce from each station a plurality of pairs of quasi-orthogonal laser scanning planes capable of reading bar code symbol orientated with bar code elements arranged in either a substantially vertical (i.e. picket-fence) or substantially horizontal (i.e. ladder) configuration with respect to the horizontal scanning window of the system.
Another object of the present invention is to provide such a bioptical holographic laser scanning system, wherein the second laser scanning station employs mirror groups and scanning facets having only low elevation characteristics and zero skew angle characteristics so as to produce from each station a plurality of pairs of quasi-orthogonal laser scanning planes capable of reading bar code symbol orientated with bar code elements arranged in either a substantially vertical. (i.e. picket-fence) or substantially horizontal (i.e. ladder) configuration with respect to the horizontal scanning window of the system.
Another object of the present invention is to provide such a bioptical holographic laser scanning system, wherein the fourth laser scanning station employs mirror groups and scanning facets having only high elevation characteristics and zero skew angle characteristics so as to produce from each station a plurality of laser scanning planes capable of reading bar code symbol orientated with bar code elements arranged in either a substantially vertical (i.e. picket-fence) configuration with respect to the horizontal scanning window of the system.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein the plurality of pairs of quasi-orthogonal laser scanning planes are produced using S-polarized laser beams directed incident the holographic scanning disc.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein four symmetrically placed visible laser diodes (VLDs) are used to create the plurality of pairs of quasi-orthogonal laser scanning planes.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein a single VLD is used to create the vertical window scan pattern, thereby minimizing crosstalk.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein the sizes of the laser beam folding mirrors employed at each laser scanning station of the present invention are minimized.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein blocking of light return paths by the laser beam folding mirrors has been eliminated.
Another object of the present invention is to provide a bioptical holographic laser scanning system,wherein mechanical interference between individual laser beam folding mirrors within the system has been eliminated.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein the angles of incidence of the laser scanning beams at the horizontal scanning window have been optimized.
Another object of the present invention is to provide a bioptical holographic laser scanning system which generates a laser scanning pattern providing 360 degrees of scan coverage at a POS station, while the internal mirror-space volume of the scanning system has been minimized.
Another object of the present invention is to provide such a bioptical holographic laser scanning system, wherein the xe2x80x9csweet spotxe2x80x9d of the 360 laser scanning pattern is located at and above the center of the horizontal (i.e. bottom) scanning window, regardless of the item orientation or location of the bar code on the item.
Another object of the present invention is to provide such a bioptical holographic laser scanning system, wherein the center of all groups of laser scanning planes generated by the system is directed toward the center of the horizontal scanning window, or to a line normal to the horizontal scanning window at the center thereof, thereby enhancing operator productivity by providing the feedback xe2x80x9cbeepxe2x80x9d at substantially the same location above the horizontal scanning window for each and every item being scanned.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein the size of the scan data collecting photodetector at each laser scanning station is minimized.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein the location of the scan data collecting photodetector at each laser scanning station is determined using a novel spreadsheet-based design process that minimizes the vertical space required for placement of the parabolic light collection mirror beneath the scanning disc.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein the size, shape and orientation of the scan data collecting photodetector at each laser scanning station is designed so that the lateral shift of the reflected beam image across the light sensitive surface of the photo detector, as a scanned item moves through the DOF region if of the scanning station, results in a relatively uniform light level reaching the light sensitive surface of the photodetector.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein use of the shift of the image across the data detector (as the item moves through the DOF region) to minimize the variation in signal.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein partial facet-to-facet DOF overlap to optimize the DOF region while minimizing the effects of paper noise; and
Another object of the present invention is to provide a bioptical holographic laser scanning system, which allows the same facets to be used for both the horizontal and vertical windows even though the distances to the items to be scanned is different for the two windows.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein use of a 12 facet disk design to increase the signal level for a 6 inch disk, necessary for POS scanners, which must provide lower laser power levels at the scan windows.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein use of an S-polarized beam at the disk to maximize signal and provide better resolution throughout the DOF region.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein use of skew facets with symmetric Left/Right skew, which allows the same scan pattern to be produced by both the fore and aft scanning stations.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein the vertical-window horizontal scan lines and the operator-side-station horizontal scan lines are split and tilted for enhanced scan coverage.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein recessing selected portions of the scanner base plate allow reduction of the box height.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein parabolic mirror with modified, non-sector-shaped, cross-section maximize light collection efficiency.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein use of optimum skew angle for each of the skew facets provides maximum scan coverage while minimizing the mirror-space volume.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein diffraction angles are selected to provide maximum scan coverage while still allowing complete blockage of the facet from undesired ambient light.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein fixed beam blocker with optimum shape prohibits ambient light from entering the facets at the zero order beam angle, which light would otherwise be directed to the data detector by the parabolic mirror, thereby increasing the noise level.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein undercut box design allows for a smaller scanner footprint in both the X-dimension and the Y-dimension.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein turning the VLD off when the scan line is no longer in the window, thereby eliminating unwanted internal. scattering of the laser light and extends the life of the laser.
Another object of the present invention is to provide a bioptical holographic laser scanning system capable of generating a complex of pairs of quasi-orthogonal laser scanning planes, each composed by a plurality of substantially-vertical laser scanning planes for reading bar code symbols having bar code elements (i.e. ladder-type bar code symbols) that are oriented substantially horizontal with respect to the bottom scanning window, and a plurality of substantially-horizontal laser scanning planes for reading bar code symbols having bar code elements (i.e. picket-fence type bar code symbols) that are oriented substantially vertical with respect to the bottom scanning window.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein each scan data collecting photodetector is positioned behind a beam folding mirror having a small hole formed therethrough to allow the return light from a parabolic mirror beneath the scanning disc to reach the photodetector, thereby enabling optimum placement of the photodetector and nearly maximum use of the surface of the beam folding mirror for light collection while providing a light shield for the data detector.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein the light collection efficiency of each scanning facet is optimized in order to compensate for variations in facet collection area during laser scanning operations.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein a beam deflecting mirror is supported on the back side of each parabolic collection mirror, beneath a notch formed therein, to allow an incident laser beam, produced beyond the scanning disc, to be directed through the light collection mirror and onto the point of incidence of the scanning disc during scanning operation.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein a single beam folding mirror is used as the last outgoing mirror to produce a plurality of different laser scanning planes that are projected out through the vertical scanning window, thereby allowing greater light collection for a given amount of space (or potentially less space).
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein a light pipe or other light guiding structure can be used to conduct collected light at a point of collection within the system, and guiding such light to a photodetector located at a convenient location within the system.
Another object of the present invention is to provide a bioptical holographic laser scanning system, wherein a light-collection cone can be used to reduce the size of the photodetector.
Another object of the present invention is to provide a bioptical holographic laser scanning system which produces a three-dimensional laser scanning volume that is substantially greater than the volume of the housing of the holographic laser scanner itself, and provides full omni-directional scanning within the laser scanning volume.
A further object of the present invention is to provide such a bioptical holographic laser scanning system, in which the three-dimensional laser scanning volume has multiple focal planes and a highly confined geometry extending about a projection axis extending from the scanning windows of the holographic scanning system.
A further object of the present invention is to provide such a bioptical holographic laser scanning system, in which laser light produced from a particular holographic optical element reflects off a bar code symbol, passes through the same holographic optical element, and is thereafter collimated for light intensity detection.
A further object of the present invention is to provide such a bioptical holographic laser scanning system, in which a plurality of lasers simultaneously produce a plurality of laser beams which are focused and scanned through the scanning volume by a rotating disc that supports a plurality of holographic facets.
A further object of the present invention is to provide such a bioptical holographic laser scanning system, in which the holographic optical elements on the rotating disc maximize the use of the disk space for light collection, while minimizing the laser beam velocity at the focal planes of each of the laser scan patterns, in order to minimize the electronic bandwidth required by the light detection and signal processing circuitry.
A further object of the present invention is to provide a compact bioptical holographic laser scanning system, in which substantially all of the available light collecting surface area on the scanning disc is utilized and the light collection efficiency of each holographic facet on the holographic scanning disc is substantially equal, thereby allowing the holographic laser scanner to use a holographic scanning disc having the smallest possible disc diameter.
A further object of the present invention is to provide such a bioptical holographic laser scanning system, in which laser beam astigmatism caused by the inherent astigmatic difference in each visible laser diode is effectively eliminated prior to the passage of the laser beam through the holographic optical elements on the rotating scanning disc.
A further object of the present invention is to provide such a bioptical holographic laser scanning system, in which the dispersion of the relatively broad spectral output of each visible laser diode by the holographic optical elements on the scanning disc is effectively automatically compensated for as the laser beam propagates from the visible laser diode, through an integrated optics assembly, and through the holographic optical elements on the rotating disc of the holographic laser scanner.
A further object of the present invention is to provide such a bioptical holographic laser scanning system, in which a conventional visible laser diode is used to produce a laser scanning beam, and a simple and inexpensive arrangement is provided for eliminating or minimizing the effects of the dispersion caused by the holographic disc of the laser scanner.
A further object of the present invention is to provide such a bioptical holographic laser scanning system, in which the inherent astigmatic difference in each visible laser diode is effectively eliminated prior to the laser beam passing through the holographic optical elements on the rotating disc.
A further object of the present invention is to provide such a bioptical holographic laser scanning system, in which the laser beam produced from each laser diode is processed by a single, ultra-compact optics module in order to circularize the laser beam produced by the laser diode, eliminate the inherent astigmatic difference therein, as well as compensate for wavelength-dependent variations in the spectral output of each visible laser diode, such as superluminescence, multi-mode lasing, and laser mode hopping, thereby allowing the use of the resulting laser beam in holographic scanning applications demanding large depths of field.
A further object of the present invention is to provide such a bioptical holographic laser scanning system, in which an independent light collection/detection subsystem is provided for each laser diode employed within the holographic laser scanner.
A further object of the present invention is to provide such a bioptical holographic laser scanning system, in which an independent signal processing channel is provided for each laser diode and light collection/detection subsystem in order to improve the signal processing speed of the system.
A further object of the present invention is to provide such a bioptical holographic laser scanning system, in which a plurality of signal processors are used for simultaneously processing the scan data signals produced from each of the photodetectors within the holographic laser scanner.
A further object of the present invention is to provide such a bioptical holographic laser scanning system, in which each facet on the holographic disc has an indication code which is encoded by the zero-th diffraction order of the outgoing laser beam and detected so as to determine which scanning planes are to be selectively filtered during the symbol decoding operations.
A further object of the present invention is to provide such a bioptical holographic laser scanning system, in which the zero-th diffractive order of the laser beam which passes directly through the respective holographic optical elements on the rotating disc is used to produce a start/home pulse for use with stitching-type decoding processes carried out within the scanner.
These and other objects of the present invention will become apparent hereinafter and in the Claims to Invention.